Raspovic et al. Journal of Foot and Ankle Research 2012, 5:25http://www.jfootankleres.com/content/5/1/25
RESEARCH Open Access
Reduction of peak plantar pressure in peoplewith diabetes-related peripheral neuropathy: anevaluation of the DH Pressure Relief Shoe™Anita Raspovic1*, Karl B Landorf1, Jana Gazarek2 and Megan Stark3
Abstract
Background: Offloading plantar pressure is a key strategy for the prevention or healing of neuropathic plantarulcers in diabetes. Non-removable walking casts, such as total contact casts, are currently considered thegold-standard for offloading this type of wound. However, alternative methods for offloading that are more costeffective and easier to use are continually being sought. The aim of this study was to evaluate the capacity of theDH Pressure Relief Shoe™ to offload high pressure areas under the neuropathic foot in diabetes.
Methods: A within-subjects, repeated measures design was used. Sixteen participants with diabetic peripheralneuropathy were recruited and three footwear conditions were evaluated in a randomised order: a canvas shoe(the control), the participants’ own standard shoe, and the DH Pressure Relief Shoe™. The primary outcome waspeak plantar pressure, measured using the pedar-X® mobile in-shoe system between the three conditions.
Results: Data analysis was conducted on 14 out of the 16 participants because two participants could notcomplete data collection. The mean peak pressure values in kPa (±SD) for each condition were: control shoe 315.9(±140.7), participants’ standard shoe 273.0 (±127.1) and DH Pressure Relief Shoe™ 155.4 (±89.9). There was astatistically significant difference in peak plantar pressure between the DH Pressure Relief Shoe™ compared to boththe control shoe (p = 0.002) and participants’ standard shoe (p = 0.001). The DH Pressure Relief Shoe™ decreasedplantar pressures by 51% compared to the control shoe and by 43% compared to participants’ standard shoe.Importantly, for a couple of study participants, the DH Pressure Relief Shoe™ appeared unsuitable for day-to-daywearing.
Conclusions: The DH Pressure Relief Shoe™ reduced plantar pressures more than the other two shoe conditions.The DH Pressure Relief Shoe™ may be a useful alternative to current offloading modalities used in clinicalmanagement of diabetic foot ulceration. However, clinical trials are needed to test their effectiveness for ulcerhealing and to ensure they are useable and safe for patients in everyday activities.
BackgroundFoot ulceration in diabetes has been recognised as amajor medical, social and economic problem all over theworld [1]. This is not surprising given that approxi-mately 15% of people with diabetes will develop a footulcer in their lifetime and that resolution of foot ulcersis often a lengthy and complex process [1]. The burdenfoot ulceration places on health care systems globally issubstantial, with 85% of all diabetes-related amputations
* Correspondence: [email protected] of Podiatry and Lower Extremity and Gait Studies Program, LaTrobe University, Bundoora, Melbourne, 3086, AustraliaFull list of author information is available at the end of the article
being preceded by a foot ulcer [2]. Significant adversepsychological consequences may also result, includingdiminished psychosocial adjustment to illness, alteredsatisfaction with personal life, poorer health-relatedquality of life and depression [3].Localised tissue trauma, in the presence of clinically-
significant sensory neuropathy, is an important risk fac-tor for chronic plantar foot ulceration in people withdiabetes [1]. Although, the complex role of biomechan-ics in diabetes-related foot ulceration is not fully under-stood, elevated dynamic peak plantar pressure is astrong risk factor for future ulceration, particularly whenoccurring in conjunction with loss of protective
al Ltd. This is an Open Access article distributed under the terms of the Creativeommons.org/licenses/by/2.0), which permits unrestricted use, distribution, andiginal work is properly cited.
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sensation [4]. It stands to reason, therefore, that offload-ing or reducing elevated peak plantar pressure is import-ant for the successful management of plantarneuropathic foot ulceration in diabetes. A robust body ofevidence supports this notion as illustrated by recenthigh-quality reviews of the literature [5-7].The salient clinical issue is not whether to use offload-
ing in the management of neuropathic ulceration, butwhat type/s of offloading modality will achieve the bestresult in light of the clinical situation and broader pa-tient context. A wide range of offloading modalities arecurrently available, with studies finding that the abilityof these devices to reduce pressure ranges from 20% to80% when compared to a control [7]. However, a barrierexists to evidence-based offloading practice due to therebeing limited research and guidelines for offloading mo-dalities, with the exception of total contact casts (TCCs)and other irremovable cast walkers [5]. A study by Wuet al. (2008) showed that the currently accepted goldstandard for offloading, the TCC [5,8], was being usedregularly by less than 2% of practitioners surveyed, suggest-ing there are important barriers to the implementationof best-practice offloading [9]. In some instances thismay be associated with issues such as lack of trainingand limited experience with the application of TCCs. Inother cases it is likely that there are mitigating circum-stances where offloading modalities such as TCCs maynot be suitable. Factors such as patient preference, clin-ical presentation, mobility requirements and socialstigma may make use of TCC difficult. In cases whereTCCs and other irremovable cast walkers are not appro-priate for use, selecting offloading modalities based onevidence is challenging due to the paucity of research.Alternative methods for off-loading that are effective,
economical, easy to use and have little impact on thepatient’s lifestyle are continually being sought. The DHPressure Relief ShoeTM is one such alternative, however tothe authors’ knowledge, evidence evaluating its effective-ness at off-loading plantar pressure does not exist. Theaim of this study was to evaluate the capacity of the DHPressure Relief ShoeTM to offload high pressure areasunder the neuropathic foot in diabetes.
Table 1 Participant characteristics (N = 14)
Characteristic Value
Age in years: mean ± SD (range) 65.4 ± 3.3 (48 to 81)
Gender (No.) 13 male : 1 female
Weight in kilograms: mean ± SD (range) 97.2 ± 15.5 (59 to 108)
Diabetes duration in years: mean ± SD (range) 22.7 ± 3.8 (3 to 48)
Previous ulceration 4 yes : 10 no
Note: two cases were excluded due to missing data (footwear issues),therefore the final analysis was conducted on 14 participants.
MethodsParticipantsThis study used a within-subject, repeated measures de-sign. Approval was granted from two Institutional EthicsCommittees and informed consent was obtained fromall participants prior to their participation in the study.Sixteen participants were recruited to the study, 15 maleand 1 female. This sample size was pre-specified andwas based on an 80% probability of detecting a clinicallymeaningful difference between interventions of 100 kPa
in peak plantar pressure (standard deviation of 100 kPaand alpha set at 0.05), using an appropriate formula[10].Participants were recruited via advertisements and directapproach from a local university podiatry clinic and ahospital-based, outpatient high-risk foot service.Participants were included if they were male or female
aged over 18 years and had either a history of, or activeplantar neuropathic ulceration. Those perceived at fu-ture risk of ulceration were also eligible – risk of ulcer-ation has been defined by Armstrong et al. as acombination of a vibratory perception threshold >25 Vand monofilament testing of four imperceptible sites,which has shown to be a highly sensitive and specificmethod for detecting risk of ulceration [11]. Four parti-cipants reported a past history of foot ulceration andone of these participants presented with a current plan-tar foot ulcer.Participants were excluded from the study if they were
found to have active infection at the wound site, distin-guished by the cardinal signs of warmth, redness, pain,tenderness, induration and purulent exudate. Partici-pants were also deemed ineligible if they required theuse of a walking aide, had current pain or injury unre-lated to the ulceration that affected walking, had anulcer from other causes, had more than one digit ampu-tated or were unable to speak basic English. Those withacute Charcot’s neuroarthropathy, determined by theclinical signs of unilateral swelling, elevated skintemperature, erythema and joint effusion were alsoexcluded from participating in the study. The character-istics of participants are shown in Table 1.
Footwear conditionsAll participants were measured in the following threefootwear conditions:
(ii) the participants’ own standard footwear;(iii) the DH Pressure Relief ShoeTM, Royce Medical
(now the DH Offloading Post-op ShoeTM, Ossur, CA).
The canvas shoes (Figure 1) were selected as theirlightweight construction and flat, thin and flexible soles
Figure 1 Canvas Dunlop Volley™ (control) shoe.
Raspovic et al. Journal of Foot and Ankle Research 2012, 5:25 Page 3 of 8http://www.jfootankleres.com/content/5/1/25
were considered to have minimal influence on plantarpressures across participants [12]. The participants’ ownstandard footwear (Figure 2) consisted of the shoes theparticipant wore most regularly and ranged from stand-ard, extra-depth flat lace-up shoes to customised be-spoke footwear. The purpose of this footwear conditionwas to establish pressure offloading properties of standardfootwear to enable a direct comparison to the DHPressure Relief ShoeTM. If the participant wore insolesor orthoses that were additional to any insoles thatcame with the shoe, these were removed prior tomeasurement.The final shoe condition was the DH Pressure Relief
ShoeTM (Figures 3a and 3b), which is a relatively new off-loading device designed for people with high pressure orulceration on the plantar surface of the foot. The DHPressure Relief ShoeTM is designed for short-term (one tofour months) use in the treatment of plantar wounds,such as diabetes-related neuropathic ulceration. The
Figure 2 Example of a participant’s standard shoe.
inside of the DH Pressure Relief ShoeTM consists of aninsole comprised of hexagonal-shaped plugs, made fromthree layers that are a combination of mixed densitymaterials including PORON® (Figure 3b). The plugs are15 mm thick and have a Velcro undersurface to keepthem firmly in place but enables their removal over theareas of high pressure as required. The upper of the DHShoe is a soft synthetic fabric, which is fastened to thefoot with large Velcro straps (Figure 3a). For this study,the plugs were removed either under the site of active orprevious plantar forefoot or midfoot neuropathic ulcer-ation, or if the participant did not present with a historyof neuropathic ulceration, under the right 1st metatarso-phalangeal joint, as this is widely accepted as one of themost common sites for neuropathic ulceration [13].
RandomisationTo minimise potential ordering effects, the three footwearconditions were tested using a random order sequence,
a.
b.
Figure 3 (a) DH Pressure Relief Shoe™ (b) Insole of DH Pressure Relief Shoe™ with hexagonal plugs removed from under the right firstmetatarsophalangeal joint.
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generated using Microsoft Excel. The participants andinvestigators collecting the pressure data could not beblinded to the testing condition that was being assessedin respective trials. However, as the plantar pressure ap-paratus produces objective data, the investigatorsthought this would have minimal impact.
Pressure measuring equipmentPlantar pressures were measured with the in-shoe pedar-X® system (Novel GmbH, Munich, Germany), a reliable,valid and accurate measure of in-shoe pressure [14,15].The pedar-X® insoles are approximately 2 mm thick andconsist of 99 capacitive pressure sensors that arearranged in a grid alignment. Plantar pressure data weresampled at a frequency of 50 Hz. All insoles had beencalibrated with the trublu® calibration device prior to
the commencement of the study (Novel GmbH, Munich,Germany).
Measurement protocolThe appropriately sized pedar-X® insole was placed ineach shoe condition (i.e. under the foot) for measure-ment. Prior to the first walking trial of each condition,the pressure insoles were zeroed as described by themanufacturer’s guidelines (Novel GmbH, Munich, Ger-many). After a familiarisation period of approximately2 minutes, participants completed three walking trialsfor each condition. Participants were timed as theywalked at a comfortable self-determined speed along a10 m walkway. If a trial did not fall within 5% of the ori-ginal walking time, it was eliminated and repeated tominimise the effect of altered walking speed on plantarpressures [16]. To exclude the effect of acceleration and
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deceleration steps, only the middle steps from each trialof the foot undergoing measurement were included foranalysis. An average recording was determined from ap-proximately nine steps (i.e. three steps from three trials)for each condition. In order to meet the independencerequirement for statistical analysis, data from only onesite on one foot was selected from each participant foranalysis [17].
Outcome measuresThe primary outcome measure was peak plantar pres-sure underneath the selected high pressure site, for eachcondition. Peak pressure was chosen due to its import-ance in indicating offloading effectiveness and thus clin-ical utility. To evaluate if alterations in peak pressureunder the mask of interest (i.e. where the DH PressureRelief ShoeTM plugs were removed) might be attribut-able to changes in weight bearing area of the plantarsurface of the foot, contact area between shoe condi-tions was analysed as a secondary outcome. We alsomeasured contact time for the whole foot in order tocross check consistency of walking speed.
Statistical analysisThe plantar pressure data were processed through theNovel-win® program (version 20.3.30). A Novel maskwas applied to identify the nominated high pressure site,which formed the primary area for comparison acrossthe three shoe conditions. Data for the variables peakplantar pressure (within mask), contact area (whole foot)and contact time (whole foot) were extracted for analysisusing the Statistical Package for the Social Sciences (SPSS)Version 18.0 (SPSS Inc., Chicago, IL). The data wereexplored for normality of distribution prior to inferentialanalysis and was within normal limits. One-way repeatedmeasures analysis of variance (ANOVA) with Bonferroni-adjusted post hoc t-tests were used to compare measure-ments between each of the shoe conditions. Comparisonswere considered statistically significant if p < 0.05.
ResultsContact time (whole foot)To cross check if participants walked at a consistentspeed during the trials, differences in whole foot contacttime based on the pedar data were evaluated betweenthe three shoe conditions (Table 2). Whilst regularity ofwalking speed was ensured within ± 5% by the data col-lection protocol, verification using pedar data was alsoundertaken due to the important effect of walking speedon peak plantar pressure [16]. No statistically significantdifference between contact times (i.e. walking speed) forthe whole foot (F2-12 = 2.350, p = 0.138) were found.Therefore, it can be assumed that any differences in
plantar pressures can be attributed to the conditionsbeing analysed.
Peak pressure differences (mask)Tables 2 and 3 provide data related to peak pressurechanges according to shoe condition. A statistically sig-nificant difference in peak plantar pressure was foundbetween shoes (F2-12 = 11.813, p = 0.001). The DHPressure-relief ShoeTM reduced peak plantar pressures by117.7 kPa compared to the standard shoe and 160.5 kPacompared to canvas shoe. This equates to a decrease inpeak pressure of 43% and 50% respectively. When com-pared to the canvas shoe, which was included as the‘control’ condition, the participant’s own shoes decreasedpeak pressure by 42.9 kPa or 14% on average, althoughthis did not reach statistical significance.
Contact area (whole foot)A statistically significant difference in contact area forthe whole foot was found between shoes (F2-12 = 5.360,p = 0.022). Post hoc tests revealed that there was a sig-nificant difference in whole foot contact area betweenthe DH Pressure-relief ShoeTM and canvas shoe (meandifference of 10.8 cm2). This increase in contact areaequates to the plantar surface of the foot having a 9%larger weight bearing area with the DH Pressure-reliefShoeTM compared to the canvas shoe. There were no dif-ferences between the DH Pressure-relief ShoeTM and thestandard shoe, or the canvas shoe and standard shoe.
DiscussionThe aim of this study was to evaluate the capacity of theDH Pressure Relief ShoeTM to offload high pressure areasunder the neuropathic foot in diabetes. The DHPressure-relief ShoeTM was selected for investigation inthis study as it is currently being marketed and used foroffloading plantar foot ulceration in diabetes. To theauthors’ knowledge, there has been no independent re-search that has previously investigated the capacity ofthe DH Pressure Relief ShoeTM to reduce pressure. Incontrast, the DH Pressure WalkerTM, Royce Medical (nowthe Active Offloading WalkerTM, Ossur, CA) a relatedproduct in a below-knee walker style, has been investi-gated previously [18,19]. The DH Pressure Relief ShoeTM
is a less bulky version of the DH Pressure WalkerTM. It isalso light, easy to fit and use, and is cost effective ataround AUS $100 per unit. Of particular interest is theinsole design in the DH Pressure Relief ShoeTM, whichallows for customisation of offloading by the selective re-moval of the hexagonal-shaped plugs over high pressuresites. The DH Pressure Relief ShoeTM is designed as a re-movable intervention and while in some clinical circum-stances this might be preferable, research has shown
Table 2 Mean, standard deviation and standard error for contact time, peak pressure and contact area for each shoecondition (N = 14)
Contact Time (m/s) (whole foot) Peak Pressure (kPa) (mask) Contact Area (cm2) (whole foot)
Mean SD Mean SD Mean SD
Canvas 684.5 101.5 315.9 140.7 116.8 20.5
Standard 672.9 88.5 273.0 127.1 124.9 31.7
DH shoe 699.3 96.9 155.4 89.9 127.6 26.7
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non-removable offloading to be associated with superiorhealing rates [18-20].In this study the DH Pressure Relief ShoeTM was
shown to reduce mean peak plantar pressure by 117.7kPa when compared to standard shoes and 160.5 kPawhen compared to canvas shoes. This equates to a 43%and 50% reduction respectively, which is comparable inmagnitude to studies using specific types of paddingand insoles [21,22]. While there is no established pres-sure cut-off point or threshold above which ulcerationwill occur, a relationship has been shown to existwhereby the greater the pressure the higher the ulcerrisk [11]. With this in mind, we believe that thisamount of pressure reduction is clinically important.We powered our study to detect a 100 kPa reduction(or difference between shoes) and the amount of reduc-tion offered by the DH Pressure Relief ShoeTM was wellabove this. Therefore, the removable plug design insolethat is integral to the DH Pressure Relief ShoeTM showspromise for offloading focal plantar pressure. Accord-ingly, this device may be useful for the treatment ofneuropathic ulcers, in the event that these results carryover into trials that use healing as a primary outcome.It is important to note that the investigators in this
project had some concerns about the fixation of the DHshoe in its current form and the stability of some partici-pants while walking. In two cases the ankle straps didnot sit flat, which may potentially cause rubbing and irri-tation to the skin. In another case the medial heel coun-ter was pushed down substantially during gait due to thehigh degree of rigid foot deformity, rendering the shoetoo unstable to be worn during extended periods of
Table 3 Comparison between the shoe conditions for peak pr
Peak pressure (mask)
Mean difference in peakpressure in kPa (95% CI)
% differencebetween shoes #
p-
Canvas /Standard
42.9 (−35.6 to 121.3) 14% decrease 0
Canvas /DH shoe
160.5 (60.1 to 261.0) 51% decrease 0
Standard /DH shoe
117.7 (40.1 to 186.3) 43% decrease 0
# A decrease in the % indicates that the second shoe recorded a lower pressure thahigher pressure than the first.
walking. Suitability of this device as an offloading modal-ity for some participants was questioned, particularlywhen dealing with a sub-population known to be at riskof falls. In addition, the aesthetics of the device may be alimitation to its acceptance by some patients. Therefore,the DH Pressure Relief ShoeTM may be a useful alterna-tive to current off-loading modalities but further clin-ical trials are warranted to determine its safety ineveryday activities and relative contraindications.Several possible explanations exist as to why peak pres-
sures were substantially reduced by the DH Pressure Re-lief ShoeTM. Due to the relatively thick and cushioningmake-up of the DH Pressure Relief ShoeTM insoles, it islikely that the plantar surface of the foot sinks into thematerials to redistribute force. This, in combination withthe removal of the plugs over pressure sites, may explainthe levels of offloading recorded. We also found a statis-tically significant difference in whole foot contact areawhere the DH Pressure Relief ShoeTM had a 9% greatercontact area than the canvas shoe. However, this resultdid not extend to differences in contact area between theDH Pressure Relief ShoeTM and standard shoe.Interestingly, peak pressure values in the patients’ own
shoes (i.e. the standard shoe condition) did not differstatistically from the canvas control shoe. This finding isconsistent with the 2007 evidence-based guidelines ofthe International Working Group on the Diabetic Foot,which recommend that standard or therapeutic footwearalone should not be used for offloading during ulcertreatment as better modalities are available [7]. It shouldbe noted, however, that the participant’s own shoes wereincluded only to allow comparison of plantar pressures
essure and contact area (N = 14)
Contact area (whole foot)
value Mean difference in contactarea in cm2 (95% CI)
% differencebetween shoes #
p-value
.473 8.1 (−4.9 to 21.1) 7% increase 0.336
.002 10.8 (2.1 to 19.4) 9% increase 0.014
.001 2.7 (−9.1 to 14.5) 2% increase 1.000
n the first and an increase in the % indicates that the second shoe recorded a
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experienced in routinely worn footwear with the DHShoe. It was not the intention of this study to evaluatefootwear as an alternative offloading device.Our findings should be interpreted in light of the
study limitations. Firstly, we measured peak pressure,not healing, as a primary outcome measure and resultscannot be directly extrapolated. Pertinent issues that ef-fect healing, such as compliance, functional effectivenessof the device and health-related quality of life, would notbe borne out by this study design. Secondly, the studywas not designed as a randomised controlled trial, it wasan initial exploration of the effects of the DH PressureRelief ShoeTM on plantar pressure. A larger, high-qualityrandomised trial with a comparison group is nowneeded to evaluate the effectiveness of the DH PressureRelief ShoeTM on ulcer healing. Finally, despite the pedar®
system being valid and reliable, it only measures forcesacting vertical to the pedar® insole and it is likely thatthe forces that shoes exert against the plantar surface ofthe foot are more complex in nature. As the pressure-mapping insoles had to contour the inside of each shoecondition tested, rather than lie flat, they only record re-sultant force [23,24]. As such, the shear component ofsuch forces are not recorded and some inherent meas-urement errors are likely to occur [23,24].
ConclusionsThe DH Pressure-relief ShoeTM reduced peak plantarpressure more than the other two shoe conditionstested. Accordingly, it may be beneficial for the treat-ment or prevention of neuropathic ulcers and may be auseful alternative to current off-loading modalities usedfor diabetic foot ulceration. Clinical trials are nowneeded to establish the impact of the device on ulcerhealing and prevention, and to ensure they are useableand safe for patients in everyday activities.
Competing interestsTwo authors listed on this publication are members of the Editorial Board ofthe Journal of Foot and Ankle Research. KBL is currently in the position ofDeputy Editor and AR is a member of the Editorial Board. It is journal policythat editors are removed from the peer review and editorial decision makingprocesses for papers they have co-authored.
Authors’ contributionsAR participated in the inception and design of the study, the data collection,contributed to statistical analysis, and drafted the manuscript. KBLparticipated in the inception and design of the study, contributed to thestatistical analysis, and drafted the manuscript. JG undertook participantrecruitment and participated in data collection. MS undertook participantrecruitment and participated in data collection. All authors read andapproved the final manuscript.
AcknowledgementsAnita Spring, Dominic Sandilands and Arthur Garoufalis from theDepartment of Podiatry, Northern Health, Melbourne, Australia.This project was funded by a research grant from Northern Health,Melbourne, Australia.
Author details1Department of Podiatry and Lower Extremity and Gait Studies Program, LaTrobe University, Bundoora, Melbourne, 3086, Australia. 2Department ofPodiatry, The Northern Hospital, 185 Cooper Street, Epping, Melbourne 3076,Australia. 3Private Podiatrist, The Melbourne Sports Medicine Centre, Level 4,250 Collins Street, Melbourne 3000, Australia.
Received: 8 May 2012 Accepted: 3 September 2012Published: 1 October 2012
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doi:10.1186/1757-1146-5-25Cite this article as: Raspovic et al.: Reduction of peak plantar pressure inpeople with diabetes-related peripheral neuropathy: an evaluation ofthe DH Pressure Relief Shoe™. Journal of Foot and Ankle Research 20125:25.
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